KARACHI (BLOOMBERG) - China's Assistant Foreign Minister Wu Jianghao has called Pakistan's ambassador in Beijing "to express extremely grave concern" over the explosion outside a Confucius Institute on Tuesday (April 26).

The apparent terror attack on a vehicle in Pakistan's southern financial hub of Karachi blast killed at least four people, including three Chinese citizens.

The three were teachers, said the Chinese foreign ministry in a statement on Wednesday.

It said China demanded Pakistan "immediately make thorough investigation of the incident, apprehend and punish the perpetrators to the full extent of the law, and take all possible measures to ensure the safety of Chinese citizens in Pakistan and prevent such incidents from happening again".

Geo television broadcast CCTV footage of the incident claiming a woman detonated the bomb near the car.

Pakistan's Interior Minister Rana Sanaullah said the attack was "deplorable and condemnable", and the government will ensure the safety of foreign nationals at all costs.

Pakistan has been witnessing a resurgence in terrorist attacks since August last year when the Taliban took over in Afghanistan, emboldening other militant groups, including their local offshoot Tehreek-i-Taliban Pakistan.

In August, a suicide bomber targeted a convoy of vehicles carrying Chinese nationals at Gwadar in southwest Balochistan province, while nine China citizens were killed in July in a bomb attack at a bus transporting workers to a dam project in the northwest.

Pakistan's newly elected Prime Minister Shehbaz Sharif, who took power this month, has said he is keen to pursue the second phase of the China Pakistan Economic Corridor under President Xi Jinping's Belt and Road Initiative.

Projects worth about US$60 billion (S$83 billion) were completed in the first phase that started in 2015.